Python Programs using functions and classes

Ex 1. Write a Python program to compute area of circle using function and a return statement.

Solution :

def areaCircle(r):

      PI= 3.14

      result=PI*r*r

      print("The result of circle: ")

      return result

Output

In [12]:

areaCircle (10)

The result of circle:

Out[12]: 314.0

Ex 2. Passing a List

Python program

def fun(numbers):

      numbers.append("DDD")

my_list = *"AAA","BBB", "CCC"+

fun(my_list)

print(my_list)

Output

['AAA', 'BBB', 'CCC', 'DDD']

Ex 3. Local and Global Variable

For example 

a=10 # a is Global Variable

def My_Function(b):# b is Local variable

      c=30 # c is Local variable

      print("b = ",b)

      print("c=",c)

Output

In [14]:

My_Function (20)

print("a = ",a)#a still exists

print("b = ",,b)#being Local variable, it does not exist outside function

print("c = ",,c)#being Local variable, it does not exist outside function

b = 20

C = 30

a = 10

‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒

                                                                   Traceback (most recent call last)

NameError

Cell In[14], line 3

        1 My_Function(20)

        2 print("a = ",a)#a still exists

‒‒‒‒> 3 print("b = ",b)#being Local variable, it does not exist outside function

        4 print("c = ",c)

NameError: name 'b' is not defined

Ex 4. Simple Class:

ClassDemo.py

class Student:

      name="AAA"  ←Data Member

      def display(self):   ← Method

            print ("The name of the student is ",self.name)

s1=Student()    ←Object: an instance of a class

s1.display()

Output

Program explanation:

In above code, we have defined one class in which there is single data member and single method.

Note that by the statement

      s1=Student()

the instance s1 is created.

Then using the instance of a class followed by dot operator which is followed by the name of the function, we can call the function defined in the class. The function display is called using the instance variable and dot operator.

Ex 5. Constructor

ClassDemo.py

class Student:

def _init_(self,name,marks):

      self.name=name

      self.marks=marks

def display(self):

      print("Name: ",self.name)

      print("marks: ",self.marks)

s1=Student("AAA",10)

s2=Student("BBB",20)

print("Student 1:")

s1.display()

print("Student 2:")

s2.display()

Output

Ex 6

Write a Python program to create a class 'Rectangle'. Also find the area and perimeter of the rectangle when length and breadth values are initiated.

Solution :

Rectangle Demo.py

class Rectangle:

      def _init_(self,breadth,length):

            self.breadth=breadth

            self.length=length

def area(self):

      print(self.breadth *self.length)

def perimeter(self):

      print(2*(self.breadth+self.length))

a=int(input("Enter length of rectangle: "))

b=int(input("Enter breadth of rectangle: "))

obj=Rectangle(a,b)

print("Area of rectangle: ")

obj.area()

print("Perimeter of rectangle: ")

obj.perimeter()

Output

Ex 7. Returning Instances

RectanglePoint.py

class Point:

      x=0

      y=0

class Rectangle:

def _init_(self,length, breadth): #constructor

      self.length=length

      self.breadth=breadth

def find_center_point(rect): #This method is outside the class

      p=Point()

      p.x=rect.length/2

      p.y=rect.breadth/2

      return p #returning instance of class Point

a=int(input("Enter length of rectangle: "))

b=int(input("Enter breadth of rectangle: "))

obj=Rectangle(a,b)

pt=find_center_point(obj)

print("Point(x,y) = (",pt.x,",",pt.y.")")

Output

Ex 8. Public and Private Memebers

StudentDemo.py

class Student:

def __init__(self,R,N): //These are the public members of class Student

self.Roll=R

self.Name=N

obj=Student(101,"Jayashree")

print("Roll No: ",obj.Roll)   #Accessing public variable outside the class

print("Name:",obj.Name)

Output

Ex 9. Public and Private Memebers

StudentDemo.py

class Student:

    def _init_(self,R,N):

        self._Roll=R  #private variable 'Roll'

        self.___Name=N  #private variable 'Name'

obj=Student(101,"Jayashree")

print("Roll No: ",obj. Roll) #trying to access private attribute

                                         #outside the class and that will cause error

Output

Program explanation: In above program,

1) There are two private variables ‒ Roll and Name. Note that to make these variables private they are written using the prefix as double underscore.

2) When we try to access these variables outside the class using the object of that class, it gives an Attribute error. Refer the screenshot for the output.

Ex 10. Printing Objects

MethodDemo.py

class Time:

    hour=0

    minute=0

    second=0

    def display(t): #Method defined inside the class

        print('%.2d:%.2d:%.2d' % (t.hour, t.minute, t.second))

time=Time()

time.hour=11

time.minute=58

time.second=20

Time.display(time)#Method is called using object of class

Output

11:58:20

Program explanation: In above program,

1. We have created a class named Time.

2. The display method is defined for this class. Note that this definition is inside the class.

3. The object or instance of the class Time is created in variable time.

4. Using the object time we invoke the method display with the help of dot operator. Hence we get the output as the values of data attributes ‒ Hour, minute and second.